CVE-2026-9571

Deactivated user accounts can continue to obtain valid OAuth access tokens via refresh token grant in Mattermost

MEDIUM

6.5

CVSS Score

Published: July 13, 2026 at 07:50 AM UTC

Updated: July 15, 2026 at 05:17 AM UTC

2 products affected across 1 vendorMattermost ServerMattermost

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Severity

MEDIUM6.5

Exploit prediction

EPSS 0.3%

SSVC

No known exploit

Description

Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to invalidate OAuth refresh tokens upon user account deactivation, which allows a deactivated user or an attacker in possession of a valid refresh token to obtain new functional access tokens via the OAuth refresh token grant endpoint.. Mattermost Advisory ID: MMSA-2026-00680

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Mattermost Server · Mattermost

95%

10.11.0 ≤ v < 10.11.2011.6.0 ≤ v < 11.6.511.7.0 ≤ v < 11.7.3

Affected range stops below 10.11.20, so it looks safe — our inference, not a vendor statement

Affected range stops below 11.6.5, so it looks safe — our inference, not a vendor statement

Affected range stops below 11.7.3, so it looks safe — our inference, not a vendor statement

Mattermost · Mattermost

60%

10.11.0 ≤ v ≤ 10.11.1911.6.0 ≤ v ≤ 11.6.411.7.0 ≤ v ≤ 11.7.210.11.0 11.6.0 11.7.0

Vendor states this is fixed in 10.11.20 (unaffected)

Vendor states this is fixed in 11.6.5 (unaffected)

Vendor states this is fixed in 11.7.3 (unaffected)

Vendor states this is fixed in 11.8.0 (unaffected)

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

https://mattermost.com/security-updates

References (1)

Vendor Advisory

Source: cverecord

https://mattermost.com/security-updates

SSVC — Action Prioritization

SSVCNo known exploitNot automatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

6.5MEDIUM[email protected]

Attack Vector: NETWORK
Complexity: LOW
Privileges: LOW
User Interaction: NONE
Scope: UNCHANGED
Confidentiality: HIGH
Integrity: NONE
Availability: NONE

Vector?

Quick Info

StatusANALYZED

CWE

CWE-305

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